Multiband Sensing for Cognitive Radios

A key aspect of cognitive radios is the need to sense the spectrum for the presence of primary users. Detection sensitivity for sensing is determined using worst case models for multipath and shadowing which makes it difficult (if not impossible) to achieve. Cooperation between cognitive radios has been advanced as a technique to alleviate some of these sensing requirements and meet the target probability of harmful interference. Unfortunately, cooperative gains are based on independence assumptions; when these assumptions do not hold the impact is on the primary user. Furthermore, cooperation causes us to miss opportunities. Ideally, we would like detection sensitivity to be specified dynamically based on actual shadowing and multipath. In this project we aim to achieve this by calibrating the sensitivity level for a given primary by using sensing measurements from nearby frequencies [1]. This proposal is based on the fact that shadowing correlation between nearby frequencies is extremely high and that multiple primaries are actually co-located on the same tower. Multiband sensing allows radios to overcome noise uncertainty based SNR walls and achieve target harmful interference values. Furthermore, multiband sensing allows the system to "qualify radios." Cooperation between qualified radios enables the system to reduce the probability of harmful interference as well as the probability of missed opportunity.